Disk drives are commonly used in microprocessor based electronic devices, such as workstations, personal computers, laptops and other computer systems, to store and retrieve large amounts of data. A typical disk drive includes a plurality of magnetic disks that are rotated by a spindle motor and an actuator arm assembly that includes read/write heads mounted to flexure arms. An actuator motor (e.g., voice coil motor) can rotate the flexure arms and heads about a pivot bearing relative to the disks. The heads are configured to fly upon air bearings in very close proximity to the rotating disks.
The surface of each disk is divided into a series of data tracks which are spaced radially from one another across a band having an inner diameter and an outer diameter. The data tracks extend circumferentially around the disks and store data in the form of magnetic flux transitions on the disk surfaces. Each data track is divided into a number of data sectors that store fixed sized blocks of user data. Embedded among the data sectors on each track are servo fields that define servo information that enables the disk drive to control the radial position of the heads relative to tracks on the disks and to determine the circumferential location of the heads.
The servo fields are written to the disks during the manufacture of a disk drive using a highly precise servo track writer, which utilizes the heads of the disk drive to write the servo fields. Because the servo fields are used to define the radial locations of tracks and the location of data along a track, it is important to precisely control the locations on the disk surfaces at which the servo fields are written. Thus, a typical servo track writer includes a precise clock signal generator and an additional recording element that is used to write a reference clock pattern on a disk surface responsive to the clock signal. The reference clock pattern is then read back from the disk surface by the additional recording element to generate a disk reference clock signal synchronized to the rotation of the disks, which is used to determine where to write the servo fields through the read/write heads onto the disks.
Using the additional recording element and manufacturing processes for writing the reference clock pattern on the disk before writing the servo fields can increase the time, cost and possibility of damage during the manufacture of a disk drive. Accordingly, there is a need for an improved approach for generating a reference clock signal that is synchronized to disk rotation and for writing servo fields responsive thereto.